Method of producing a piston blank containing an annular insert



Oct. 14, 1969 s. STAUSS 3,471,914

METHOD OF PRODUCING A PISTON BLANK CQNTAINING AN ANNULAR INSERT Filed Sept. 8, 1967 INVENT OR Siegfried Szauss 3,471,914 METHOD OF PRODUCING A PISTON BLANK CONTAHNTNG AN ANNULAR INSERT Siegfried Stauss, Stuttgart-Wangen, Germany, assignor to Mahle Kmm.-Ges., Stuttgart-Bad Cannstatt, Germany Filed Sept. 8, 1967, Ser. No. 666,349 Claims priority, application Germany, Oct. 1, 1966, M 71,136 Int. Cl. B23p 15/10 U.S. Cl. 29156.5 3 Claims ABSTRACT OF THE DISCLGSURE To make an annular channel in the piston head of a light metal piston, it is customary to cast an insert into a lightweight casting, which insert corresponds to the annular channel and is composed of a material that can be removed from the piston by means which does not impair the piston material. A piston blank is produced from this casting and then the insert partially exposed by drill holes through which a medium is introduced that dissolves the insert. The annular channel thus formed is customarily used for the circulation of a cooling agent in the finished piston.

Holding pins composed of a metal having a higher melting point than that of the light metal are used to hold the insert in place during the casting of the light metal in a mold. Heretofore, these holding pins have remained in the piston and thus had to be composed of a material which was not affected by the medium used to dissolve the insert. For example, the pins were composed of a high nickel content steel alloy.

The disadvantage has been found that the steel pins have a much higher specific weight than the light metal of the piston and they are therefore subject to stronger forces than occur on the mass of the piston during the operation of the piston and that this causes the pins to become loose and in some cases fall out. When such occurs, the cooling agent drains from the annular channel and enters the cylinder and, in some cases, the combustion chamber and moreover the displaced steel parts can cause severe damage to the engine.

It would seem that such disadvantages could be avoided by using holding pins composed of a material having the same specific weight as the piston metal. However, such pins would melt and combine with the light metal being cast over the insert and therefore would fail as holding pins. Consequently, the prevailing thought is that alloyed steel holding pins must be used and attempts have been made to produce a joint by shaping the pins to prevent the pins from falling out. However, such only retarded the loosening and falling out of the pins, but in the long run did not prevent such from occurring.

In this invention, the above disadvantages are avoided by holding the insert in place in the casting mold by using pins having a higher melting point than that of the casting, as before. However, after the casting has solidified and before it is forged, the pins are pulled out and nited States Patent 0 ice are replaced with light metal plugs composed of, for example, pure aluminum, which at least partially fill the holes which formerly contained the pins and which holes are preferably first bored or drilled. It is of especial advantage to use plugs which are shorter than the length of the holes and which are placed in the holes spaced both from the insert and from the exterior surface of the piston so that spaces remain in the holes on each side of the plugs. Then, when the casting is forged, the holes are filled with the plugs and closed with the plug material firmly embedded in the piston.

The holes in the inserts formed by pulling out the holding pins are preferably closed by means of short pins made from the same material as the insert or of a material just as soluble as that of the insert before the metal plugs are put in the holes.

The holding pins used for holding the insert in place during the casting can be manufactured of common steel or any other suitable material which is not affected by the material forming the casting.

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying drawings, in which:

FIGURE 1 is a cross-sectional view through a solidified casting containing the insert;

FIGURE 2 is a view similar to a portion of FIGURE 1 showing the insertion of the plugs; and

FIGURE 3 is a cross-sectional view through the forged piston blank.

In FIGURE 1, the light metal casting 1 is composed of an aluminum or aluminum alloy and has embedded therein an annular insert 2 composed of copper. In order to hold the insert 2 in place in the mold during casting, holding pins 3 composed of steel have been used which extend through the casting into the insert 2. After the casting has solidified and removed from the mold, these holding pins are pulled out of the casting.

As shown in FIGURE 2, the removal of the pins 3 leaves holes 4. Preferably these holes are partially drilled to form holes 5 of a larger diameter than the original holes 4. Light metal plugs 6 are then inserted into the holes 5 so as to leave spaces between the insert and the plugs and the plugs and the exterior surface of the piston. Preferably insert pins 6a composed of copper or the like are first inserted in the holes left in the insert 2 by the removal of the pins 3.

As shown in FIGURE 3, the casting has been forged into a piston blank 7. The spaces on each side of the plugs 6 have been forged closed with a deformation of the shape of the plugs 6. The forging also welds the material of plug 6 with the material of the piston so that they are tightly sealed in the piston. As the plug material has the same or at least very close to the same weight material, there is no fear that the plug material will become loose during the operation of the piston.

The piston blank 7 is then drilled to partially expose the inserts 2 so that the inserts can be etched out of the blank. The blank is then machined to form the finished piston.

Having now described the means by which the objects of the invention are obtained,

I claim:

1. A method for forming a piston blank composed of a light metal and containing a circular insert composed of a material having a higher melting point than that of the insert and being adapted to be etched out later to make an annular channel in the piston comprising casting the light metal around an insert held in place by high melting point holding pins, solidifying the casting and removing said holding pins, placing light metal plugs in the holes left in the piston by the removal of 3 4 the pins, and then forging said casting including said References Cited plugs to form a piston blank in which said plugs are FOREIGN PATENTS forged in and close said holes.

912,256 12/1962 Great Bntam. 2. A method as in claim 1, said plugs bemg of less 1,326,289 3/1963 France.

length than said holes and being spaced in said holes both from said insert and the exterior of said casting 5 JOHN CAMPBELL Primary Examiner before said blank is forged.

3. A method as in claim 2, further comprising closing SHORE Asslstant Exammer the holes in said insert with insert pins composed of the US. Cl. X.R.

same material as said insert. 10 29-423 

